The present disclosure relates to a thin planar light-emitting module.
Conventionally, many fluorescent lamps or bulbs have been used as a lighting tool for illumination. In recent years, to reduce power consumption and extend service life, various white light-emitting devices using a light-emitting diode have been developed as substitutes for such a lighting tool.
The light emitted from a light-emitting diode has strong directivity and a small emission area. Thus, it is difficult to illuminate a wide range with uniform luminance using a single light-emitting diode. Therefore, a lighting tool fabricated by arranging a plurality of light-emitting diodes may be considered. But a large luminance unevenness is produced between the area right above the light-emitting diode and the area above a peripheral part. In order to reduce the illuminance unevenness, a diffusing lens or a diffusing sheet is provided above the light-emitting face of the light-emitting diode. However, such a diffusing lens or a diffusing sheet disadvantageously reduces the light quantity and increases the cost of the lighting tool.
In this connection, JP-A-2007-287448 (JP '448) discloses a lighting device having a lens for guiding light from a light source, wherein an air layer for increasing the angle created by the light emitted from the light source and the main light beam axis of the light source is disposed between the entrance face of the lens and the outside surface as the light-emitting face. Because the air layer can cause light emitted from the light source to reach a wide region, uniform luminescence can be achieved on the light-emitting face.
In the technique described in JP '448, light emitted from the light source is merely transmitted through a lens and therefore, although illuminance unevenness on the light-emitting face may be improved, elimination of color unevenness is not attained.